The Uniqueness of our Universe

A Physicist’s Point of View

Dr. Paul Ohmann

University of St. Thomas

November 30, 2012

What can Science tell us?

Experiments and Observations: We discover facts.

• Facts are interpreted through our senses.

• Facts should be testable and reproducible.

Theory: We build models to understand facts.

• Models explain how facts are related leads to understanding

• Models are tested by further experiments subject to change

Scientific Process

Anthropic Coincidences

Observation: Universe is amazingly conducive to life

Anthropic Coincidences ways in which Universe characteristics are tuned to support life

Questions:

• Are these “coincidences” really “coincidences” or must Nature evolve with these characteristics?

• What role might random chance play in the characteristics of the Universe?

• Would life arise in many types of Universes?

• Do the Anthropic Coincidences suggest a Creator?

Anthropic Coincidences

1. Strengths of the Fundamental Forces

Strong Nuclear Force ~ 102 EM Force ~ 105 Weak Nuclear Force ~ 1038 Gravity

Interplay between Strong Nuclear and EM Force:

Consider Helium protons try to break nucleus apart

Weaker strong force or stronger EM force less stability

Heavier atoms are particularly susceptible:

Our Universe: Heaviest (relatively) stable element U (92 protons) If EM force were 10 times stronger Heaviest element: Ne (10 protons)

No Ca, no Fe…. life would be drastically different!

Anthropic Coincidences, cont.

Stellar Formation:

proton – proton cycle: 1H + 1H 2H + e+ + 2H + 1H 3He + 3He + 3He 4He + 2 1H

Then 3He, 4He, and H make Li, Be, B

Suppose the strong force…

Net reaction: 4 1H 1 4He + 26.7 MeV

…were 10% weaker: 2H unstable no elements heavier than H !!

no sunlight !!

…were 4% stronger additional reactions: 1H + 1H 2He

n + n 2n

Anthropic Coincidences, cont.

Why is a stronger Strong Force bad?

1H + 1H 2H + e+ + Current Universe: is a weak nuclear interaction

proceeds slowly: stars live a long time

Alternate Universe: 1H + 1H 2He is a strong nuclear interaction

proceeds quickly: stars rapidly burn out

The weak nuclear interaction is needed to give life time to develop!

Anthropic Coincidences, cont.

2. Flatness of Space/Cosmological Constant

Key Idea: Big Bang expansion must not be too fast or too slow

Too fast: Stars/galaxies wouldn’t form no life!

Too slow: Universe would gravitationally collapse

Current Age of Universe: 13.75 billion years…and still expanding

“Fine tuning” needed to account for Universe age/content:

Expansion rate (Cosmological constant): 1 part in 10-120

Curvature of Space (Flatness): 1 part in 10-35

3. Proton stability

Anthropic Coincidences, cont.

Unstable proton no stable Hydrogen Stellar Formation? Water?

Question: Why are protons stable? (Neutrons are unstable!)

epn allowed: ~ 15 minutes

enp disallowed Why?

Answer: neutrons are a bit heavier than protons! mn = 939.6 MeV/c2

mp = 938.3 MeV/c2

Question: Why does mn > mp? No one knows….

Anthropic Coincidences, cont.

4. Matter/Antimatter Asymmetry

Early Universe Highly symmetric (we think)

But perfect symmetry: matter + antimatter light

Current Universe: # matter > # antimatter by 1 in 109 necessary for life!

Science: Matter/Antimatter Asymmetry “CP Violation”

e.g. K0 decay: sdsdKL 2

1

sdsdKS 2

1

~ 5.2 x 10-8 s

~ 0.9 x 10-10 s

e

eKL

slightly favored

Anthropic Coincidences: Summary

1. Strong Force must be between 0.90 and 1.04 of current value

2. EM Force cannot be much stronger than its present value

3. Expansion must allow for galaxies/stars without Universe collapsing

4. Proton stability

5. Matter/Antimatter Asymmetry

For life to exist in the Universe:

Question: Did we just get lucky???

Evidence for God?

• Anthropic Coincidences

• Wouldn’t a Creator want life to arise? (Strong Anthropic Principle)

• First Cause of Universe (Aquinas)

• Big Bang

• Natural Laws

Question: Are there scientific alternatives?

Scientific Explanations: Anthropic Coincidences

1. Lucky Hypothesis.

Universe evolved by chance into a form conducive for life

2. Necessary Hypothesis.

Universe was required to evolve into its present form

3. Many Universes Hypothesis.

Many Universes (or domains) exist, with varying laws and initial conditions.

Weak Anthropic Principle: Obviously we’re in a Universe conducive to life!

Final Thoughts

Many Universe Hypothesis: untestable?

Observable Universe: Natural laws seem consistent

Other Domains: Inherently unobservable? (Conjecture: Interference Ripples in CMB)

Creator Hypothesis: untestable?

God works through Natural Laws with few exceptions (none that seem scientifically testable)

Philosophical evidence: Consciousness/Free Will/Rational Thought(Can these arise from purely material entities?)

Personal evidence: Untestable no control group

Science: Gives an appreciation for the special nature of the Universe

Extra Slides

Symmetries

Noether’s Theorem: Symmetries = Conservation Laws

Action Principle (Phys 331): 2

1

0t

t

dtL

External Symmetries: related to particle motion (any type of particle)

L = T - V

conservationp

translation invariance symmetry

0

1xdtp

mx

x0 arbitrary

conservationL

rotation invariance symmetry

0

1 dtLI

θ0 arbitrary

E conservation time invariance symmetry

Invariance of L under appropriate symmetry something is conserved

Symmetries, continued

Internal Symmetries: related to particle intrinsic nature (particle-dependent)

Electric Charge (QED) conservation U(1) symmetry

Weak Charge conservation SU(2)L symmetry

Strong Charge (QCD) conservation SU(3) symmetry

Baryon # conservation (e.g. p, n)

Lepton # conservation (e.g. e, )SU(3) x SU(2)L x U(1) symmetry

Note: U(1), SU(2)L, and SU(3) are groups (Math 301-2)

Quantum Field Theory particle = field relate particles to forces

Symmetry of L under group transformation ei(x)Q

yields conservation laws (Q = generator of appropriate group)

Higher Symmetry?

Grand Unified Theories:

Incorporate lower symmetries into one larger symmetrye.g. SU(3) x SU(2)L x U(1) SU(5)

Fundamental Assumption: Universe is simple

But: Universe of today many distinct symmetries

Guess: Early Universe has one large symmetry

Original symmetry “broken” as universe cooled

Suppose this is true.

Question: Why must there be this original symmetry?

Science: This is a tough question!

Aquinas: First Cause God

Anthropic Coincidences, cont.

5. The 3- process: Production of 12C

Life Cycle of a Star:

Hydrogen phase proton-proton cycle:

1H + 1H 2H + e+ + 2H + 1H 3He + 3He + 3He 4He + 2 1H

Helium phase 3- process:

hydrogen depleted gravitational collapse core heating

[Note: = 4He]4He + 4He + 4He 12C + 7.3 MeV

Problem: Negligible probability of 3 nuclei simultaneously colliding!

Consider 2-step process: 4He + 4He 8Be8Be + 4He 12C

Problem: 8Be highly unstable: ~ 10-16 s

Question: How can we produce 12C?

Anthropic Coincidences, cont.

Resonance 12C happens to have a resonance at 7.7 MeV…and 8Be + 4He reaction is just energetic enough (with thermal energy) to hit resonance!

4He + 4He 8Be8Be + 4He 12C*(7.7 MeV)

Equilibrium condition:

But also: 12C* 12C + 7.7 MeV leakage from system

Conclusion: Without 7.7MeV (± 0.3 MeV) resonance No 12C !!

Resonance = big increase in production rate!

Further reaction: 12C + 4He 16O just 0.04 MeV above resonance!

Enough 12C for carbon-based life!